<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var num = prompt('请输入班级人数：');
        var sum = 0;
        var average = 0;
        for (i = 1; i <= num; i++) {
            var score = prompt('请输入第' + i + '个学生的成绩');
            sum += parseFloat(score);
        }
        alert('班级的总成绩为：' + sum);
        average = sum / num;
        alert('班级的平均成绩为：' + average);
    </script>
</head>

<body>

</body>

</html>